You're crossing into a nebulous area when you attempt to connect
reality and methodology (better known as the twilight zone where the
whole court is out of order). In the same vane, we could debate the
fact that 80+% of fire are controlled by no more than 3 sprinklers and
ask why have a 1500 sf remote area (or even 900 sf with QR). Bottom
line is that we have X amount for sprinkler (that exceed the actual
demand) and a simultaneous Y amount for hose demand (for those cases
that have some mop-up) producing the only reality that counts - that
being that it works. Occasional variances are granted to reduce the
hose demand but in looking at it, I'm having a difficult time
connecting those dots. What is the relevance of having 1500 gpm hose
demand when discussing the ability to supply the sprinkler and a
reduced hose demand unless you plan to turn off the sprinklers and run
only a manual response? Apples to oranges. I Like them both but not
together.
Roland
On Jun 30, 2011, at 8:43 AM, Ron Greenman wrote:
It was just rhetorical. I was thinking what if I'm boosting the tank
pressure to just what I need (think steepish curve) to operate the
sprinks
at the 450 gpm. That gets the 1500 gpm to the hydrant at over 0 psi
and the
engine takes it to whatever the FD wants. So I'm showing a steep
drop in
pressure with supply and a rise in demand to almost the magic line.
Then I
have to add the horizontal 250 gpm and I'm slightly north of the
supply
curve. Easy enough to fix with a better designed pump but why should
I have
to fix it? As for gpm the tank has sufficient capacity to cover
duration for
both hydrant and system operating simultaneously so I meet that
water supply
quantity demand in spades. Why do I need to include that 250 gpm
when I have
more than enough water for simultaneous operation? What if that pump
that
will do the job without adding the hose stream is cheap and forcing
the
addition of the hose stream increases my cost? Why do I need to
spend the
money for a different pump to flatten a curve that meets need? And
why do I
need to add it if I have one tank but not if two tanks? This has
mostly to
do with what is on the piece of paper and that horizontal line from
450 gpm
to 700 gpm and how that interacts with the other diagonal line heading
downhill and to the right. The pump is undersized to cover the
pressure at
the gpm required when this extra and arbitrary 250 gpm is added to
the curve
but the 250 gpm is covered by the 1500 gpm and engine psi boost at the
hydrant, and would be OK if each was supplied by it's own tank (the
hydrant
is only on the pump because it and the building and a future
building are 10
feet higher than the base of the tank and the the single pump (which
will be
sized to handle the extra code required 250, but the tank is
oversized and
capacious enough to cover both buildings burning and using the
hydrant at
the same time for an hour) is the cost-effective. It just struck me
as one
of those things that could happen (the supply pressure issue).
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